Thursday, April 3, 2008

mating mice help to locate emotion causing genes in humans

A recently published study in the open-access journal PLoS ONE reported that during sexual interactions with female mice, male mice emit high-frequency calls. Researcher Haoran Wang (University of Toronto) found that the calls are linked to approach behaviors and genes that are in charge of positive emotions.

In the scientific community it has long been assumed that emotions and other personality traits and disorders are correlated across family members. It has not been easy to find out which genes play a role in controlling emotions. mice are useful in studies concerning human genetic behaviour, since humans and mice have similar numbers of genes. Mice genes can be added or deleted, where as humans cannot. Researchers have been able to analyze mouse behaviors to establish associations between genes with complex behaviors.

Researchers used the number and density of different male and female vocalizations to index the emotional responses of mice. The calls were measured using special microphones and computer programs, since they are in audible to humans. During the courtship phase males often made simple whistles or modulated calls. Then, the vocalizations became more complex "chirp-like" calls after mounting the females. The sounds increased in complexity and number and the intesity of the mouse increased.

Single genes relating to the neurotransmitters dopamine and acetylcholine were then deleted. It was then found that there was a significant reduction of male calls. These neurotransmitters are important for emotional expression in humans and rats. Esspecially when the M5 and M2 acetylcholine receptor genes were deleted a reduced number of male vocalizations noticed. This led to a change in the duration, frequency, and bandwidth of the calls.

Mutations in the M4 muscarinic receptor and D2 dopamine receptor were not associated with a change in the number of vocalizations unlike the previous two. It was found that these mutations changed the length of calls.

Wang said that, "This work has supported the theory, proposed by Jeffrey Burgdorf and Jaak Pansepp, that 50-kHz calls reflect positive affect in rats, and extended that theory to higher-frequency mouse calls."

The researchers also recorded a role for dopamine when they found that the street drug amphetamine, at low doses, activates the brain dopamine system and induces a "chirp-like" call. Male mice that did not have the M5 receptor gene that is important for activating dopamine neurons and therefore did not manifest the chirp.

It was then concluded that their results may offer a new way to screen for emotion genes and to develop drugs for controlling emotions, drug abuse and mood disorders.